It is thought to chew food longer can prevent people overeating by giving the brain more time to receive signals from a full stomach or satiety.

It can also lower the levels of ghrelin, the 'hunger hormones' circulating in the digestive system.

In this study, researchers at Harbin Medical University, China, recruited 16 lean men and 14 obese teenagers in their late teens and 20s, and conducted two trials.

The first experiment, researchers wanted to see if obese male participants chew food differently than slim male participants. Each participant was given a cake and filmed with a secret camera to test how many times they chewed before being swallowed.

The results found that although obese men chew at the same rate as lean men, obese men swallow food much faster, in other words just chew a few times.

In the second experiment, both groups were each given a cake and asked to chew as much as 15 times and then swallowed. And researchers found that when participants chewed longer they consumed 11.9 percent fewer calories, regardless of whether they were lean or obese.

Blood tests taken 90 minutes after eating with 40 chewing also showed participants having a much lower ghrelin level than when they chewed 15 times.

The results of this study have been published in the American Journal of Clinical Nutrition